Detector for clogged filters

ABSTRACT

A clogged filter detector has a transmitter and a sensor which are held in place by a transmitter bracket and a sensor bracket, respectively. The transmitter emits a beam of electromagnetic radiation, and the sensor is positioned in the path of this beam at a point such that the beam travels through a filter between the transmitter and the sensor. The transmitter and sensor are mis-aligned with the air flow at the point where the beam contacts the filter. The transmitter alternates between a transmitting mode and a dormant mode, and the transmitter emits a plurality of electromagnetic pulses during each transmitting mode.

A. CROSS REFERENCE TO OTHER APPLICATIONS

This application is a continuation of and therefore claims priority to,and the benefit of, currently pending U.S. patent application Ser. No.13/457,952 filed Apr. 27, 2012, titled “Detector for Clogged Filters.”

B. FIELD OF THE INVENTION

The present invention relates to detectors for determining when airfilters have become clogged.

C. BACKGROUND AND DESCRIPTION OF THE RELATED ART

Filters for heating, ventilation, and air conditioning (HVAC) systemsplay an important role by minimizing deposits of dust and otherparticles on cooling coils and heating surfaces. Deposits of dust orother materials on cooling coils and heating surfaces reduce theefficiency, and therefore increase the energy needed to operate the HVACsystem. A clogged filter can result in decreased air flow over coolingcoils and heating surfaces, and decreased air flow also lowersefficiency and can shorten the life of a HVAC system because the HVACsystem has to run longer to maintain the desired temperature.

After a period of use, dust accumulates on the filters, causing them tobecome clogged and requiring additional energy consumption. At somepoint, it becomes cost-effective to remove the filter and either cleanit or replace it with a new one. HVAC equipment manufacturers typicallystate their warranties so that the user, not the manufacturer, isresponsible for equipment failures due to neglect in maintaining thesystem. Manufacturers typically emphasis maintenance of the dustfilters. In most cases, the manufacture does not have access to anoperating HVAC system unless called by the user, so it is not practicalfor a manufacturer to be responsible for filter maintenance. It oftentakes weeks or months before an air filter needs to be cleaned orreplaced, and the long periods of time and lack of constant attentioncan result in users neglecting air filter maintenance.

Many newer, high efficiency air-conditioners and heat pumps now usevariable speed fan motors (ECM—Electronically Commutated Motors) whichattempt to achieve constant, optimized flow through the dust filter andAC or heat pump coils, even as dust gradually clogs the filter. Thefilter can, never-the-less, eventually clog sufficiently that the airflow decreases. The increased fan motor power required to draw airthrough the clogging filter decreases the HVAC efficiency. Decreasingflow across the coils below the optimum flow rate also decreases thesystem efficiency. Increases in run time due to the clogged filter canboth 1) increase energy requirements (decrease efficiency) and 2)decrease system lifetime, because HVAC system lifetime approximatesinverse proportionality to system run-time.

In recent years, the lower costs and increased accuracies ofdifferential pressure switches have led to their more frequentapplication for monitoring the clogging of dust filters. Theseinstruments monitor differential pressure between the input and outputsides of the filter. When the differential pressure reaches apredetermined level, an alarm is triggered which indicates the filter isclogged. Problems can occur from opening/closing of doors between roomsor other actions modifying ambient room pressure. Any ducting leaks,quite normal in older systems, also leads to increased flow ofnon-filtered (filter bypass) air as the filter becomes clogged. Withincrease dust loading and clogging of the dust filter, the filter willoften physically warp so that air flows around the filter; i.e., afilter bypass air-flow path is created until the filter is cleaned orreplaced.

An electro-optical dust filter sensor/alarm offers advantages over thedifferential pressure sensor in that it is not affected by the flowacross the filter or by the speed of the HVAC fan motor. Since theinvention of dust filters, the “eyeball” (visually examining thedust/dirt build-up on the filter's leading edge) has been thetraditional means of determining when the filter needs replacing orcleaning. This eyeball examination is often left to the memory of theuser, which may be aided by such things as a calendar date (i.e., thefirst of each month).

Some electro-optical based clogged dust filter detectors are designedfor use with low optical density filter media. However, a filterdetector which functions with filters designed for smaller (sub-micron)particle removal is desirable. These filters are necessarily moreoptically dense than traditional low optical density filter media, andtherefore require an optical filter detector that has increased opticalsensitivity.

One example of an optical filter detector comprises a simple lightemitting diode (LED) coupled to a receiving photo-diode (orphoto-transistor) with a simple signal processor. This filter detectormay perform the required task with the lower cost, lower opticaldensity, lower MERV (minimum efficiency reporting value) rated dustfilters. However, as the filters become more optically dense to removesmaller (few micron to submicron) particles (i.e., filters with higherMERV values), the simple optical transmitter/sensor electro-opticalfilter detectors are not sufficient.

The cheaper, lower MERV filters typically either have no pleats orpleats with a spacing of 1 to 2 pleats (folds) per inch; at least someof the high MERV filters are manufactured with a pleat spacing of up to8 pleats per inch. Thus the high MERV filters are more optically dense,especially when viewing across the pleats. Therefore the basicelectro-optical system described above may not be suitable with the highMERV, optically dense filters such as the 3M® Filtrete® 1500, 1700 or1900 brand or equivalent DuPont® filters. As stated above, high MERVfilters remove a greater percentage of small (micron and submicron)particles than the cheaper filters. This is especially important forpeople with allergies or in clean room or sterile hospital situationsrequiring “clean air”.

In order to operate with higher MERV, high efficiency (from smallparticle collection standpoint) filters, the filter detector must thushave adequate sensitivity to function with optically dense filter media.Also, since HVAC dust filters are often located in hallways with noavailable electrical power, a long-life, battery-powered filter detectorcan be desirable.

Filters can be used for a wide variety of purposes other than the HVACsystems discussed above. For example, filters are used to controlincoming dust and outgoing paint particles for paint sprayingoperations. They are also used to control dust accumulation onelectronic components for ventilated electronics enclosures such asthose used by cable television companies on the side of the street. Theclean environment used in fabrication of micro-electronic chipstypically requires a filtered air source. Very clean (filtered) air isalso required for some medical applications. These filter uses can allbe referred to as HVAC (heating, ventilation and air-conditioning)applications.

Since the filter maintenance requirement is environment driven ratherthan time driven, a clogged filter sensor is helpful in maintaining HVACsystem optimal operating efficiency. A system that notified the userwhen an air filter needed attention could minimize energy losses anddecreased performance resulting from clogged air filters.

SUMMARY OF THE INVENTION

The present invention is directed to clogged filter detection systems.These systems generally comprise an optical transmitter adapted totransmit a beam of light or other electromagnetic radiation through thebody of a filter (filter media) at least once, a photo receiver/sensorpositioned to detect the transmitted electromagnetic radiation once itpasses through the filter media, and a processor for receiving signalsfrom the receiver/sensor and communicating a notice when the level ofobscurant reaches a predetermined value.

One aspect of the present invention relates to optimization of thefilter detector to function with very (optically) dense dust filterswhich are designed to remove relatively small particles (i.e., submicronsized). Particles of this size often agitate allergy sufferers. A secondaspect of the invention relates to increased battery lifetime forbattery operated dust filter detectors.

A clogged filter detector has a transmitter and a sensor which arepreferably held in place by a transmitter bracket and a sensor bracket,respectively. The transmitter emits a beam of electromagnetic radiation,and the sensor is positioned in the path of this beam at a point suchthat the beam travels through a filter between the transmitter and thesensor. The transmitter and sensor are preferably mis-aligned with theair flow at the point where the beam contacts the filter. Thetransmitter alternates between a transmitting mode and a dormant mode,and the transmitter emits a plurality of electromagnetic pulses duringeach transmitting mode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a heating, ventilation, and air conditioningsystem.

FIG. 2 is a diagram of a filter positioned over a filter receptacle,with a combined transmitter bracket, sensor bracket, and reflectorbracket that fits onto the side of the filter, where the bracket is inposition to be slide onto the filter before placing the filter in thefilter receptacle.

FIG. 3 is a diagram of one embodiment of a filter detector where thetransmitter bracket and sensor bracket are connected to the filterreceptacle.

FIG. 4 is a diagram of a different embodiment of a filter detector wherethe transmitter and sensor brackets are one and the same, and aremounted on the wall of the duct. The reflector bracket is a differentbracket which is also mounted on the duct wall.

FIG. 5 is a series of graphs over time showing the strength of thetransmitted electromagnetic radiation in the bottom graph, the sensorreading based on the transmitted electromagnetic radiation aligned withand over the bottom graph, and the calculated clogging level alignedwith and over the sensor reading graph.

FIG. 6 is a graph over time showing the strength of the transmittedelectromagnetic radiation from the transmitter.

FIG. 7 is a schematic of one embodiment of portions of the filterdetector.

FIG. 8 is a graph of the output intensity of a transmitter compared tothe wavelength of electromagnetic radiation being transmitted.

FIG. 9 is a graph of the relative sensor sensitivity compared to thewavelength of electromagnetic radiation received.

FIG. 10 is a graph of an electrical pulse train used to power atransmitter during a transmitting mode.

DETAILED DESCRIPTION HVAC System

A heating, ventilation, and air conditioning (HVAC) system 10 typicallyincludes a filter 12 positioned in a filter receptacle 14, as seen inFIGS. 1 and 2. The filter 12 and associated filter receptacle 14 areoften positioned in a duct 16 or plenum of an HVAC system 10. The HVACsystem 10 typically includes a blower 2, a heating surface 4, coolingcoils 6, a drain pan 7, a compressor 8, return and supply vents, afilter receptacle 14, ducts 16, and other components. The filterreceptacle 14 is often positioned in a return line, and can include afilter receptacle ledge 18 that supports the filter 12 and prevents itfrom being drawn into the HVAC return ducts 14. The filter receptacle 14also can include filter receptacle side plates 20, which can beperpendicular to the filter receptacle ledge 18. The filter receptacleside plates 20 are close to the edges of the filter 12, and help forcereturning air through the filter 12 instead of going around the filter12. There can be a grill 22 positioned over the filter receptacle 14,where the air passes through the grill 22 before passing through thefilter 12. The grill 22 can isolate and protect the filter 12 from aliving area.

The filter 12 itself can have an external frame 24 that supports afilter body 26. The filter body 26 can be a mat, a flat sheet, a pleatedsheet, a plurality of stacked sheets, or a wide variety of other shapesand configurations. The filter 12 has a filter edge 28, which is oftenthe outer portion of the external frame 24, and the filter 12 also has afilter top surface 30 opposite a filter bottom surface 32. The filterbody 26 can be held in place by the external frame 24, or by a filtersupport 34, or the filter body 26 may be self supporting. The filtersupport 34 can be a lattice system of paper, paperboard, metal, or othermaterials, or it can be netting or other materials positioned over,under, and/or around the filter body 26. The filter support 34 can helphold the filter body 26 together, or just add strength and durability tothe filter 12 as a whole. The filter 12 is often a rectangular cube, inwhich case it has a filter edge 28 with four different surfaces and afilter top surface 30 opposite a filter bottom surface 32. However,other filter shapes are possible, such as discs, triangles, cylinders,or almost any shape.

During use, the HVAC system 10 forces air through the filter 12, and theair flow is typically perpendicular to the filter top surface 30 and thefilter bottom surface 32. In other embodiments, air flow can impact afilter 12 at various angles, particularly if the filter receptacle 14 isclose to a bend or corner in the duct 16. The air flow typically entersthe filter body 26 from the filter top surface 30, and exits the filterbody 26 from the filter bottom surface 32. Dust and other particulatematter gradually accumulates on the filter top surface 30 and throughoutthe filter body 26, and the accumulating dust slowly clogs the filter12. The filter 12 resists air flow more and more as dust accumulates inthe filter 12, and the accumulated dust actually serves to filter moredust from the returning air. Therefore, a dirty filter 12 may clog morerapidly than a clean filter 12, and the rate of clogging can increaseover time.

The clogged filter detector 40 shown in FIGS. 3 and 4 and describedherein can be used for HVAC systems 10, but it can also be used for manyother applications. This includes filters 12 for paint spraying systems,ventilated electronic enclosures, clean rooms for dust sensitivemanufacturing operations or other dust sensitive needs, and most otheruses that requires filters to reduce the dust entrained in air or othergases. This description is primarily directed towards a HVAC system 10,but it should be understood that this is just one possible use of theclogged filter detector 40, and this description is intended to addresssystems other than HVAC systems 10, as will be understood by one skilledin the art.

Clogged Filter Detector and Transmitter

A filter detector 40 comprises a transmitter 42 and a sensor 44, as seenin FIGS. 3 and 4, with continuing reference to FIGS. 1 and 2. Thetransmitter 42 emits a beam 46 of electromagnetic radiation, such asinfra-red light, near infra-red light, visible light, or otherfrequencies of electromagnetic radiation. The transmitter 42 willtypically emit one frequency, or a limited range of frequencies, ofelectromagnetic radiation. The transmitter 42 can be a light emittingdiode, a laser, or other sources of electromagnetic radiation.

The sensor 44 produces an electrical current when contacted byelectromagnetic radiation, and the strength of the electrical currentincreases as the sensor 44 is contacted by more electromagneticradiation. The sensor 44 can be a photo diode or a photo resistor, butother sensors known to those skilled in the art are also possible. Thesensor 44 may be sensitive to a specific frequency or range offrequencies of electromagnetic radiation, so that the sensor 44 onlygenerates an electrical current when contacted by certain frequencies ora certain range of frequencies of electromagnetic radiation. Theresponse of the sensor 44, or the strength of the electrical currentproduced per quantity of received electromagnetic radiation, is alsodependent on the frequency of the electromagnetic radiation.

Matching the frequencies of the transmitter 42 and the sensor 44 canimprove the overall sensitivity of the filter detector 40. One frequencyof electromagnetic radiation has a set wavelength, and preferably thepeak wavelength at which the transmitter 42 emits electromagneticradiation is within 200 nanometers of the peak sensitivity of the sensor44, and more preferably the peak wavelength at which the transmitter 42emits electromagnetic radiation is within 50 nanometers of the peaksensitivity of the sensor 44. In various embodiments, the peaktransmitter frequency and the optimal sensor frequency are in theinfra-red range, the near infra-red range, the visible light range, orother frequency ranges.

The transmitter 42 emits a beam 46 of electromagnetic radiation, andthis beam 46 can be directed at the filter 12 such that the beam 46strikes the filter 12 at a measurement point 48. The sensor 44 can bepositioned so this beam 46 strikes the sensor 44 after the beam 46strikes the measurement point 48 and passes through the filter 12. Asdust and other particulates accumulate on the filter 12, the strength ofthe beam 46 which passes through the filter 12 and strikes the sensor 44decreases, because the increasing accumulation of dust and otherparticulates increasingly block the beam 46. Therefore, the amount ofdust accumulation on the filter 12 can be measured by recording theamount of electrical current produced by the sensor 44 when the filter12 is clean, and comparing that to the amount of electrical currentproduced by the sensor 44 as the filter 12 gradually accumulates dust.

To simplify terminology, a “sensor reading” 45 is defined as ameasurement of the amount of electrical current produced by the sensor44, especially when the transmitter 42 is transmitting a beam 46 ofelectromagnetic radiation. A “clogging level” 43 is defined as apercentage based on the number 1 minus the ratio of the current sensorreading 45 divided by the sensor reading 45 when the filter 12 was newor freshly cleaned. One example of sensor readings 45 are shown in FIG.5, with continuing reference to FIGS. 1-4.

There is no exact amount of dust that clogs a filter 12, but the filterdetector 40 can use a set clogged level 47 as the clogging level 43 thatdefines when a filter 12 is clogged. Therefore, the set clogged level 47is the percentage reduction of the sensor reading 45 over time that isused to notify the user when the filter 12 is clogged. The filterdetector 40 can also include an alarm sensitivity adjustment 49 whichcan be used to adjust or change the set clogged level 47, and the alarmsensitivity adjustment 49 can be positioned in a wide variety oflocations on the filter detector 40 so as to be convenient for the user.For example, the alarm sensitivity adjustment 49 (as well as any otheroperating controls) can be positioned with the transmitter 42, thesensor 44, on a bracket, or even remotely, such as with a remotecomputer or other related electronic device.

The transmitter 42 can be held in place by a transmitter bracket 50, andthe sensor 44 can be held in place by a sensor bracket 52. Thetransmitter bracket 50 and the sensor bracket 52 can be connected to thefilter receptacle 14 to hold them in place when the filter 12 is removedfor cleaning or replacement. In other embodiments, the transmitterbracket 50 and/or the sensor bracket 52 can be connected to the filter12 itself, the walls of the duct 16, the grill 22, or to any otherstructure that can secure the transmitter 42 and sensor 44 in the properpositions.

The transmitter and sensor brackets 50, 52 should hold the transmitter42 and sensor 44 in a position that is mis-aligned with the air flowthrough the filter 12 at the measurement point 48, so that thetransmitter 42 and sensor 44 do not block air flow at the measurementpoint 48. Air carries entrained dust to the filter 12, and thisentrained dust gradually accumulates on the filter 12. The dustaccumulation is measured at the measurement point 48, so air flow at themeasurement point 48 should be representative of the entire filter 12.Dust accumulation is measured at this filter surface measurement point48 and also within the filter body 26 along the optical path of the beam46 between the transmitter 42 and sensor 44. Blocking air flow to themeasurement point 48 would reduce the amount of dust accumulation at themeasurement point 48. Therefore, aligning the sensor 44 or transmitter42 with the air flow through the filter at the measurement point 48could result in an inaccurate filter detector 40 because the filterdetector 40 would not accurately measure the total dust accumulation onthe largest part of the filter 12 where air flow is not obstructed.

If the air flow is perpendicular to the filter top surface 30, thetransmitter 42 can be held at a position over the filter top surface 30or adjacent to the filter top surface 30 with the beam 46 directed at anacute angle toward the filter top surface 30. This secures thetransmitter 42 to the side of the air flow through the measurement point48, so the air flow through the measurement point 48 is not obstructed.The sensor 44 can then be positioned in line with the beam 46 so thesensor 44 can also be positioned to the side of the air flow through themeasurement point 48. The transmitter 42 and sensor 44 are thenmis-aligned with the air flow through the filter 12 at the measurementpoint 48 because the transmitter 42 and sensor 44 are to the side of theair flow path through the measurement point 48 on the filter 12. Thereis frequently limited space in and around the filter receptacle 14 tomount the filter detector 40, so the transmitter 42 and sensor 44 mayhave to be close to the surface of the filter 12. This close positioningincreases the importance of mis-aligning the transmitter 42 and sensor44 with the air flow through the filter 12.

The sensor 44 should be positioned in the path of the beam 46 at a pointafter the beam 46 has passed through the filter 12. This can beaccomplished in many ways. The transmitter bracket 50 and the sensorbracket 52 hold the transmitter 42 and the sensor 44 in position, sothese brackets 50, 52 are used to position the transmitter 42 and sensor44. In one embodiment, the sensor 44 is secured on the opposite side ofthe filter 12 as the transmitter 42. This can be done by eitherpositioning the sensor 44 directly in line with the beam 48 emitted fromthe transmitter 42, or by positioning one or more reflectors 54 directlyin line with the beam 48 emitted from the transmitter 42 such that thereflectors 54 direct the beam 48 to the sensor 44. Alternatively, thetransmitter 42 and sensor 44 can be positioned on the same side of thefilter 12, and a reflector 54 can be positioned on the opposite side ofthe filter 12 directly in line with the beam 48 emitted from thetransmitter 42 such that the beam 48 is directed to the sensor 44. Morethan one reflector 54 can be used, if desired. The beam 48 has to passthrough the filter 12 at least twice when the transmitter 42 and sensor44 are on the same side of the filter 12, and this can reduce theoverall signal strength reaching the sensor 42. Some filters 12 have anexternal frame 24 that limits access to the filter top or bottom surface30, 32, so the transmitter bracket 50 and the sensor bracket 52 can beadjustable so the measurement point 48 can be moved as necessary.

In one embodiment, the reflector 54 can be a retroreflector, and thetransmitter 42 and sensor 44 can be positioned very close to each other.In this embodiment, the transmitter bracket 50 and the sensor bracket 52can be one and the same bracket. The transmitter 42 can be positionedwithin a housing, and in this embodiment it is possible for thetransmitter 42 and the sensor 44 to be positioned in the same housing.The reflector 54 can be secured in place in many ways. Some techniquesfor securing the reflector 54 include a reflector bracket 58, or thereflector 54 can be secured to the filter receptacle 14, the internalwalls of the duct 16, or even directly to the filter 12. Use of aretroreflector type reflector 54, which reflects electromagneticradiation back to the source of that electromagnetic radiation, cansimplify the positioning of the transmitter 42 and sensor 44 becausethey can be co-located.

The filter detector 40 preferably requires the transmitter 42 to emit arelatively consistent amount of electromagnetic radiation over time, sothe change in the sensor reading 45 is based on accumulated dust on thefilter 12 and not on a change in the performance of the transmitter 42.One or more batteries 60 can be used to power the transmitter 42, andthey may also be used for operation of the sensor 44 and othercomponents of the filter detector 40 requiring electrical power. If thebattery 60 loses power over time, the beam 46 emitted from thetransmitter will decrease in strength, and this will indicate the filter12 is becoming clogged. That means a dying battery 60 will falselyindicate a clogged filter 12, instead of falsely indicating a cleanfilter 12, and this can call attention to the filter detector 40 forbattery changing or charging. In some embodiments, the filter detector40 will notify the user when the battery 60 loses voltage, such as withan audible sound, a light, or by other techniques. The filter detector40 can also be powered by alternating current or direct current suppliedfrom sources other than a battery 60, such as power provided by autility company or from a generator.

The beam 46 can be polarized, and the sensor 44 can include a filterthat reduces electromagnetic radiation that is not polarized the same asthe beam 46 when the beam 46 reaches the sensor 44. This can reduceinterference from outside sources of electromagnetic radiation, such assunlight, light bulbs, or other sources. Also, the beam 46 can befocused to a narrow beam 46 to increase the amount of emittedelectromagnetic radiation that can actually reach the sensor 42, but amore narrow beam 46 requires more accurate placement of the sensor 42 toensure the sensor 42 is in line with the beam 46. A more narrow beam 46may be beneficial for more optically dense filters 12, because therelatively stronger signal strength may be necessary to sufficientlypenetrate the filter body 26.

In one embodiment, the transmitter 42 can have an aperture diameter of 5mm. In other embodiments, the aperture diameter of the transmitter 42can be approximately between 5 mm to 10 mm, but other ranges are alsopossible. In yet another embodiment, the transmitter 42 can be a laserdiode.

Controller for the Transmitter

A controller 62 can be used to control the operation of the transmitter42. The controller 62 can be electrically connected to the transmitter42, but it may also be possible for the controller 62 to utilizewireless technology, known to those of skill in the art, to control thetransmitter 42. The controller 62 can direct the transmitter 42 toalternate between a transmitting mode 64 and a dormant mode 66, as seenin FIG. 6, with continuing reference to FIGS. 1-5. The transmitter 42does not transmit significant amounts of electromagnetic radiationduring the dormant mode 66. The transmitter 42 emits the beam 46 duringthe transmitting mode 64, and the transmitter uses far more power duringthe transmitting mode 64 than during the dormant mode 62. The filterdetector 40 can save power, and thereby extend battery life if poweredby a battery 60, by using lengthy dormant modes 66 separated byrelatively short transmitting modes 64.

In one embodiment, the controller 62 can adjust and vary the length ofthe dormant mode 66 based on the sensor reading 45 during at least oneprevious transmitting mode 64. For example, the controller 62 can setthe dormant mode 66 for 72 hours if the clogging level 43 indicates thefilter 12 is less than 80% clogged, and the controller 62 can change thedormant mode 66 to 24 hours when the clogging level 43 indicates thefilter 12 is at least 80% clogged, but not more than 90% clogged. Thecontroller 62 can then change the dormant mode 66 to 6 hours when theclogging level 43 indicates the filter 12 is at least 90% clogged, andthe set clogged level 47 may be at a clogging level 43 of 95%. Thecontroller 62 can be set to change the length of the dormant mode 66when the clogging level 43 reaches one or more preset values. The presetvalues can vary for many reasons, including different users or differentapplications, and the preset values can even be adjustable by the user,if desired. There can be any number of different dormant mode lengthsbased on the clogging level 43, and there can even be an algorithm tocontinuously adjust the length of the dormant mode 66 based on theclogging level 43, if desired.

A filter 12 tends to clog relatively slowly, so frequent tests are notnecessary when the filter 12 is relatively clean. As the filter 12becomes more clogged, the length of the dormant mode 66 can be shortenedso there is not a significant delay between the time when the filter 12becomes clogged and the time for the filter detector 40 to test thefilter 12 for clogging. This can help insure a user is promptly notifiedwhen the filter 12 becomes clogged, but also helps save power whenfrequent testing is not necessary. Power saving can be particularlydesirable when the filter detector 40 is battery 60 powered, because itcan extend the battery life.

Changing the length of the dormant mode 66 can be based on one singlesensor reading 45, but the trigger to change the dormant mode 66 canalso be more than one consecutive sensor readings 45. Requiring morethan one consecutive sensor reading 45 to change the length of thedormant mode 66 can help reduce changes based on a single errantreading. Other parameters can also be used to trigger changes in thelength of the dormant mode 66, such as time and user inputs.

The controller 62 can direct the transmitter 42 to emit a plurality ofelectromagnetic radiation pulses 68 during a single transmitting mode64, where the pulses 68 are separated by periods of inactivity (referredto as off-times 69) in the transmitting mode 64. Emitting pulses 68 canhave several advantages for the transmitter 42. For example, the periodsof off time 69 between pulses 68 can help minimize and controloverheating, because the transmitter 42 does not generate heat duringperiods of off-time 69. The pulses 68 can also allow a battery 60 toregain voltage, because voltage from a battery 60 can decrease while thetransmitter 42 is emitting a beam 46, and then recover during periods ofoff-time 69. Pulses 68 can also help reduce “noise” in the sensorreading 45, because the sensor 44 will have several different readingswithin one transmitting mode 64, and these different readings can beaveraged. Background noise will tend to increase or decrease the sensorreading 45 for each individual pulse 68, but averaging the sensorreadings 45 for several different pulses 68 tends to reduce the noise,because background noise that increases one reading is cancelled out bybackground noise that decreases a different reading. Background noiseban be further decreased by increasing the number of pulses 68 in asingle transmitting mode 64.

In some embodiments, the transmitting mode 64 will be 1 second or less,and there can be 64 to 128 pulses 68 during the transmitting mode 64.The duty cycle during the transmitting mode can be about 50% or less, oreven 10% or less in alternate embodiments, where the duty cycle is theratio of the pulse 68 time to total time during the transmitting mode64. The total time during the transmitting mode 64 is the sum of thetime for the pulses 68 and the off-time 69. The length of thetransmitting mode 64, the dormant mode 66, the number of pulses pertransmitting mode 64, and the duty cycle during the transmitting mode 66can all vary for different filters 12, filter uses, and other design andoperation considerations.

Processor for the Sensor

A processor 70 can be used to control the sensor 44 and/or measure thesensor readings 45. Depending on the type and characteristics of thesensor 44 used, the processor 70 can direct the sensor 44 when tooperate, and the processor 70 can measure the amount of electricalcurrent generated by the sensor 44 and convert that measurement into thesensor reading 45. This can involve various techniques, such as but notlimited to amplifying the electrical signal, and converting theelectrical signal into a digital value. The processor 70 can beelectrically connected to the sensor 44, but the processor 70 (or atleast some components of the processor) may be wirelessly connected tothe sensor 44. In some embodiments, the processor 70 can communicatewith the controller 62, and the processor can limit operation and/orreadings from the sensor 44 to periods when the transmitter 42 isemitting a beam 46. This can include limiting operations and/or readingsof the sensor 44 to the time of the pulses 68 during the transmittingmode 64. In some embodiments, the processor 70 and the controller 62 arecombined in a single housing, and can even use shared wiring, circuits,and other components.

The filter detector 40 can include a calibration switch 72. Thecalibration switch 72 can be activated when a filter 12 is cleaned orreplaced, and this can initiate calibration of the filter detector 40.The filter detector 40 is calibrated by measuring the sensor reading 45when the calibration switch 72 is activated, and that sensor reading 45is saved as the calibration sensor reading 74. As time passes, thefilter 12 becomes more clogged, and the sensor readings 45 becomesmaller because less electromagnetic radiation passes through the filter12. The subsequent sensor readings 45 are compared to the calibrationsensor reading 74 to determine the clogging level 43 of the filter 12.As the difference in the current sensor reading 45 and the savedcalibration sensor reading 74 become larger, the clogging level 43 ofthe filter 12 increases, and the degree of clogging is associated withthe clogging level 43 of the filter 12.

In some embodiments, the filter receptacle 14 is open to sunlight orother bright lights when the filter 12 is cleaned or replaced, andsunlight or other bright lights can disrupt the accuracy of acalibration sensor reading 74. In some embodiments, the filter detector40 and the calibration switch 72 are only accessible when the filterreceptacle 14 is open. Therefore, activation of the calibration switch72 can activate the processor 70 and the controller 62 to test, measure,and record the calibration sensor reading 74 after a set calibrationdelay time interval has passed. This can give the user time to close thefilter receptacle 14 and thereby block unwanted outside interferencesduring measurement of the calibration sensor reading 74. The filter 12is still considered freshly washed, new, or freshly changed after thecalibration delay time interval has passed, because the calibrationdelay time interval is small compared to the time necessary for thefilter 12 to become clogged.

In some embodiments, there can be more than one calibration sensorreadings 74. The processor 70 and/or controller 62 can record acalibration sensor reading 74 when the calibration switch 72 isactivated, as well as recording one or more calibration sensor readings74 after the calibration delay time interval. If more than onecalibration sensor reading 74 is measured, the processor 70 or othercomponents of the filter detector 40 can use different techniques tomeasure, determine, and save the calibration sensor reading 74 used fordetermining the clogging level 43. These different techniques include,but are not limited to: (i) the average of the various calibrationsensor readings 74; (ii) the last of the calibration sensor readings 74;or (iii) when two or more calibration sensor reading measurements arewithin a set range of each other, the calibration sensor reading 74 canbe the average of the sensor readings 45 that are within the set rangeof each other.

Computer

In some embodiments, the filter detector 40 can include a computer 90,or the filter detector 40 can communicate with a separate computer 90.The computer 90 can be integrated with the controller 62 and theprocessor 70, or it can be a separate unit, or there may not be acomputer 90 at all. Some users have to maintain several differentfilters 12, and it can become challenging to keep track of all thedifferent filters 12. The processor 70 can transmit sensor readings 45or clogging levels 43 to a computer 90 to facilitate tracking of severaldifferent filters 12. There can be a plurality of processors 70 thattransmit sensor readings 45 or clogging levels 43 to the computer 90,and the computer 90 can track the values for each different processor 70and associated filter 12. The computer 90 can save the calibrationsensor reading 74 and calculate the clogging level 43 in place of theprocessor 70, and the processor steps associated with the calibrationsensor reading 74 and clogging level 43 calculations can be equallyapplicable to the computer 90. The controller 62, processor 70, andcomputer 90 are all electronic components, and they can share the samehousing and even some circuits, memory, or other components, so thesecomponents can be difficult to distinguish.

A computer 90 can store and analyze large amounts of data, and this canaid in maintaining filters 12. For example, the computer 90 can: (a)track and graph clogging levels 43 for a filter 12; (b) record HVAC orother filter maintenance, and compare the maintenance history to otherfilters, manufacturer recommendations, or other factors; and (c) recordchanges in operation or settings for the filter detectors 40. A computer90 can integrate filter maintenance and record keeping into a morecomplete maintenance record keeping system, and can be used to maintainrecords for insurance purposes. Detailed records can help control costsby allowing a user to select the most cost effective filter 12, or tocompare clogging level 43 to energy associated with a particular filter12 to determine the most cost effective maintenance practices. Theprocessor 70, controller 62, and computer 90 can communicate wirelesslyor by hardwire, and it is even possible to integrate the processor 70and/or controller 62 and/or computer 90.

In some embodiments, the filter detector 40 or the computer 90 can sendnotices 92 to the user. The notices 92 can be sent when a filter 12becomes clogged, or based on almost any other trigger point desirable.The processor 70 or computer 90 can determine a filter 12 is cloggedwhen the clogging level 43 reaches a set clogged level 47, and in someembodiments the set clogged level 47 can be adjusted by the user withthe alarm sensitivity adjustment 49. In some embodiments, a notice 92will only be sent if there are a plurality of consecutive readings thatreach a set clogged level 47. This can reduce false notices 92 based ona bug or other debris temporarily being in the path of the beam 46. If aset clogged level 47 is met in one reading, but the next reading shows aclogging level 43 below the set clogged level 47, the requirement for anotice 92 is reset to require two or more consecutive readings thatreach the set clogged level 47.

The notice 92 can be simple, such as a light that flashes and/or anaudible signal such as a beeping sound when the filter 12 becomesclogged. This simple notice 92 can be local to the filter detector 40,or remote, as desired. In other embodiments, the notice 92 to the usercan be more complex. For example, the notice 92 can be a text message,an e-mail, a telephone call, a radio call, a page, or other types ofcommunication that notifies the user that a filter 12 is clogged, orthat recommended maintenance is due, or any other notice 92 that isdesirable to the user. The notices 92 can include an indication or labelidentifying the filter 12 requiring attention (such as the filter 12with a clogging level 45 that has reached the set clogged level 47), aswell as other information such as the last time maintenance wasperformed, the type of filter 12 required, the time span the filter 12has been in service, and recorded notes relating to tools or specialconsiderations for a particular filter 12.

One embodiment of the filter detector 40 is shown in FIG. 7, withcontinuing reference to FIGS. 1-6. This shows the controller 62, theprocessor 70, and the computer 90 located within the same housing, sothe controller 62, processor 70, and/or computer 90 can be differentparts of one electronics module. In this embodiment, the controller 62comprises a voltage regulator 35 and a pulse generating switch 36, andthe transmitter 42 is a light emitting diode (LED). The beam 46 passesthrough the filter 12 and strikes the sensor 44, which is a photo diodein this embodiment. The processor 70 comprises an amplifier 37, and acombined analog—digital converter 38, microprocessor controller 39, anddigital storage chip 41 are also part of the processor 70 and/or thecomputer 90. This shows the calibration switch 72 and the alarmsensitivity adjustment 49, as well as a speaker 94, a light 96, and aradio transmitter 98 to send notices 92 to the user. Other embodimentsare also possible.

EMBODIMENTS AND EXAMPLES

In one embodiment of the present invention, the transmitter 42 can be aninfrared light emitting diode (LED). It is beneficial to match thefrequencies of electromagnetic radiation emitted by the (LED)transmitters 42 with the sensor 44, which can be a silicon receiver. Thefrequency matching provides increased optical efficiencies over filterdetectors 40 in which the peak transmitter frequency and the strongestsensor receiving frequency did not match, such as with an LEDtransmitter 42 which transmits in the red visible range and a sensor 44with a peak receiving efficiency in the near infrared.

FIGS. 8 and 9 depict properties of one embodiment of an LED transmitter42 and a photo-diode sensor 44, with continuing reference to FIGS. 1-7.The filter detector 40 works best when the peak relative LED transmitteroutput intensity 100 is a near match to the peak relative sensorsensitivity 104. The relative LED transmitter output intensity 100 isshown in FIG. 8, where the vertical axis of the graph depicts outputintensity 100 in milliwatts per steradian (mW/SR), and the horizontalaxis of the graph depicts wavelength 102 in nanometers (nm). Therelative sensor sensitivity 104 is shown in FIG. 9, where the verticalaxis depicts relative sensor sensitivity 104 and the horizontal axisdepicts wavelength 102 in nanometers (nm). Many higher sensitivity andlower cost sensors 44 are most sensitive in the infrared range around awavelength 102 of 940 nm, so the selection of an infrared transmitter 42with a maximum output intensity 100 at approximately the same wavelength102 can increase the efficiency of the filter detector 40.

Another aspect of the present invention relates to sensitivityimprovements involving transmitted beam width (i.e., beam dispersion)and sensor field-of-view. For a point source, the transmitted beam widthbetween half power points is approximately V/D, where X is theelectromagnetic radiation wavelength and D is the aperture (diameter) ofthe transmitter output optic. The transmitter output optic is often areflective parabolic or spherical surface, or a lens. In one embodiment,the aperture diameter of the transmitter is 5 mm. To take advantage of arelatively tight transmitted beam 46 (low beam dispersion), thetransmitter 42 aiming is preferably such that the center of thetransmitted beam 46 does not continuously “dance” across (or beyond) thesensor 44. In one embodiment of the filter detector 40, the transmittedbeam 46 has over double the output intensity (130 milliwatts persteradian [mW/SR] versus 60 mW/SR) of other transmitted beams 46 with awider beam dispersion, and pointing has been tested to be stable within˜ 1/10 beam width. Additional gains are achievable with transmitters 42having more narrow beams 46, or using a laser diode, provided adequatepointing is maintained.

Another embodiment of the present invention relates to the pulsedtransmitter format with a low duty cycle that can be used to allow a)the transmitter LED to cool between pulses 68 and b) to provide time forthe battery voltage to recover between pulses 68. Likewise, the sensorviewing may be synchronized to match the transmitter pulsing, whichdecreases background “noise” accumulated by the receiver.

An electrical pulse train can be used to power a transmitter LED, wherethe transmitter 42 turns the electrical pulse train into pulses 68 ofelectromagnetic radiation, as shown in FIG. 10 with continuing referenceto FIGS. 1-9. For simplicity, the electrical pulses 68 and theelectromagnetic pulses 68 are given the same reference number 68 becausethey are directly related through the transmitter 42. The electricaloff-times 69 between the pulses 68 during the transmitting mode 64 arealso given the same name and reference number as the electromagneticradiation off-times 69 between pulses 68 during the transmitting mode 64for the same reason.

Each pulse 68 has a peak voltage 106 which is reached shortly afterturn-on. From the peak voltage 106, the voltage sags until theelectrical power is turned off at the end of the pulse 68, and this sagis shown by a downward sloped line extending to the right of the peakvoltage 106 up to the point where the power is turned off at the end ofthe pulse 68. A significant off-time 69 allows the battery voltage torecover, (and the transmitter 42 to cool), provided the off-time 69 islong relative to the pulses 68. The ratio of the pulse 68 to the totaltransmitting mode 64 is called the duty cycle. A 10% duty cycle istypically adequate for battery voltage recovery.

Also, as discussed above, the averaging of the sensor readings 45 duringeach pulse 68 provides an improved signal-to-noise ratio. Therefore, aproperly designed pulsed LED transmitter 42 and synchronized sensor 44offers three advantages: (1) batter voltage recovery between pulses 68,(2) Transmitter LED cooling between pulses 68, and (3) improved signalto noise ratios from averaging sensor readings 45 from multiple pulses68. With a 1 millisecond pulse length and a 10% duty cycle, one LEDtested by the Applicant accepted up to 0.5 amp current pulses 68. Apulse length of about 1 millisecond used with this tested LEDtransmitter 42 and a photo-diode sensor 44 also provided adequate timefor a relatively low power consuming, relatively low speed (lowfrequency response) analog-digital converter 38 to acquire and processthe sensor reading 45.

Another aspect of the filter detector 40 relates to improved batterylifetime by utilizing variable dormant modes 66 between the activetransmitting modes 64. For example, if it is determined that thetransmitting modes 64 for filter tests should occur every 12 hours whenthe filter 12 nears a clogged condition, at the beginning of themeasurement sequence (i.e., shortly after the filter 12 has beeninstalled), the dormant mode 66 can be set at some higher threshold, forexample, 48 hours. As the filter 12 soils and the (filter) penetratingelectromagnetic radiation decreases, test intervals (and the associateddormant modes 66) are decreased until the measured electromagneticradiation reaches the user preselected set clogged level 47 and thenotice 92 is transmitted, which can be activation of a local and/orremote alarm.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed here.Accordingly, the scope of the invention should be limited only by theattached claims.

The invention claimed is:
 1. A clogged filter detector comprising: a. a transmitter that emits a pulse of electromagnetic radiation; b. a receiver sensor; c. a transmitter bracket connected to the transmitter, where the transmitter bracket secures the transmitter such that the pulse of electromagnetic radiation contacts a filter at a measurement point, and where the transmitter bracket secures the transmitter in a position that is mis-aligned with an air flow through the filter at the measurement point; d. a sensor bracket connected to the sensor, where the sensor bracket secures the sensor in a position that is mis-aligned with the air flow through the filter at the measurement point, and where the sensor bracket secures the sensor in the path of the transmitted pulse of electromagnetic radiation in a position such that the transmitted pulse of electromagnetic radiation passes through the filter between the transmitter and the sensor; e. a controller that controls the transmitter such that the transmitter is alternatively in a transmitting mode having an associated transmitting mode time period or a dormant mode, and where the transmitter emits a predefined number of multiple pulses of electromagnetic radiation during each transmitting mode time period; f. a non-transitory tangible media containing software or firmware encoded thereon for operation by one or more processors, wherein the one or more processors reduce the impact of background noise reflected in sensor readings by determining an average sensor reading value for the transmitting mode time period based on the sensor readings associated with the predefined number of multiple pulses within the transmitting mode time period; and wherein the dormant mode is of a variable length and wherein the controller shortens the time between variable length dormant modes based at least in part on instruction from one or more processors that the filter is nearing a clogging level.
 2. The filter detector of claim 1 where the total periods of inactivity between pulses during the transmitting mode are at least five times greater than the total time the transmitter emits a pulse of electromagnetic radiation during the transmitting mode.
 3. The filter detector of claim 1 wherein the one or more processors and the controller are connected such that the sensor is activated when the transmitter is transmitting a pulse of electromagnetic radiation.
 4. The filter detector of claim 1 further comprising: g. a calibration switch connected to the one or more processors, where the processors calibrate the filter detector at a set calibration delay time interval after the calibration switch is activated by measuring a calibration sensor reading, and where clogging level of the filter is determined by comparing the sensor reading during the transmitting mode time period to the calibration sensor reading; and wherein the filter detector transmits a notice when the measured clogging level reaches a set clogged level for two or more consecutive clogging level measurements.
 5. The filter detector of claim 1 where the transmitter is powered by a battery.
 6. A clogged filter detector comprising: a. a transmitter that emits a beam of electromagnetic radiation; b. a sensor; c. a controller that controls the transmitter such that the transmitter is alternatively in either a transmitting mode having an associated transmitting mode time period or a dormant mode, and where the transmitter emits a predefined number of multiple beams of electromagnetic radiation during each transmitting mode time period; d. a non-transitory tangible media containing software or firmware encoded thereon for operation by the one or more processors, wherein the one or more processors determine the average sensor reading value for the transmitting mode time period based on the sensor readings associated with the predefined number of multiple beams within the transmitting mode time period; and wherein the dormant mode is of a variable length and wherein the controller shortens the time between variable length dormant modes based at least in part on instruction from one or more processors that the filter is nearing a clogging level.
 7. The clogged filter detector of claim 6 further comprising: e. a transmitter bracket connected to the transmitter, where the transmitter bracket secures the transmitter such that the beam of electromagnetic radiation contacts a filter at a measurement point, and where the transmitter bracket secures the transmitter in a position that is mis-aligned with an air flow through the filter at the measurement point; f. a sensor bracket connected to the sensor, where the sensor bracket secures the sensor in a position that is mis-aligned with the air flow through the filter at the measurement point, and where the sensor bracket secures the sensor in the path of the transmitted beam of electromagnetic radiation in a position such that the transmitted beam of electromagnetic radiation passes through the filter between the transmitter and the sensor.
 8. The clogged filter detector of claim 6 further comprising a notice, where the filter detector transmits the notice when the clogging level reaches a set clogged level for two or more consecutive clogging level measurements.
 9. The clogged filter detector of claim 8 where the notice is at least one of a text message, an e-mail, or a telephone call.
 10. The clogged filter detector of claim 6 where a peak wavelength at which the transmitter emits electromagnetic radiation is within 50 nanometers of a peak sensitivity of the sensor.
 11. The clogged filter detector of claim 6 wherein the determination of whether the filter is nearing a clogging level is based at least in part on the average sensor reading value from the transmitting mode time period.
 12. A clogged filter detector comprising: a. a transmitter that is alternatively in a transmitting mode or a dormant mode, wherein the transmitter emits a predefined number of multiple pulses of electromagnetic radiation when in the transmitting mode during a transmitting mode time period; b. a sensor that produces an electrical current when contacted by a pulse of electromagnetic radiation, and where a sensor reading is based on the electrical current produced; c. a transmitter bracket connected to the transmitter; d. a sensor bracket connected to the sensor; e. a non-transitory tangible media containing software or firmware encoded thereon for operation by the one or more processors, wherein the one or more processors determine a sensor reading value for the transmitting mode time period based on the sensor readings associated with the pulses within the transmitting mode time period, and wherein the determination of whether the filter is nearing a clogging level is based at least in part on the sensor reading value from the transmitting mode time period; and wherein the dormant mode is of a variable length and the time period between variable length dormant modes based at least in part on whether the filter is nearing a clogging level.
 13. The clogged filter detector of claim 12 further comprising: f. a transmitter bracket connected to the transmitter, where the transmitter bracket secures the transmitter such that the beam of electromagnetic radiation contacts a filter at a measurement point, and where the transmitter bracket secures the transmitter in a position that is mis-aligned with an air flow through the filter at the measurement point; g. a sensor bracket connected to the sensor, where the sensor bracket secures the sensor in a position that is mis-aligned with the air flow through the filter at the measurement point, and where the sensor bracket secures the sensor in the path of the transmitted beam of electromagnetic radiation in a position such that the transmitted beam of electromagnetic radiation passes through the filter between the transmitter and the sensor.
 14. The clogged filter detector of claim 13 further comprising: h. a calibration switch connected to at least one other component of the filter detector, where the one or more processors measure a calibration sensor reading at a set calibration delay time interval after the calibration switch is activated, and where a clogging level is determined by comparing the sensor reading during the transmitting mode time period to the calibration sensor reading.
 15. The clogged filter detector of claim 14 further comprising: i. a computer, where the one or more processors transmit the clogging level to the computer; and wherein the computer transmits a notice when the clogging level reaches a set clogged level.
 16. The clogged filter detector of claim 12 wherein the sensor and the transmitter are located in separate housings.
 17. The clogged filter detector of claim 12 where a notice to the user is at least one of a text message, an e-mail message, a telephone call, a radio transmittance, and a page.
 18. The clogged filter detector of claim 17 where the notice is transmitted if the clogging level reaches the set clogged level for two or more consecutive clogging level calculations. 